Control of the temperature of superheated vapor



July 26, 1960 CONTROL OF THE .1, BLIZARD 2,946,323

TEMPERATURE OF SUPERHEATED VAPOR Filed April 13, 1953 2 Sheets-Sheet l nventor Jo/M/ 54/2/1190 Bu (Ittomeg 2 Sheets-Sheet 2 a 2 7 a Q6 a 2 C 2 x w w .4 T. a 3 2 1 lflm um m w w T 7 2 5 7. 2 I1 3 x 5 5 A i 5 0 4 T 3 5 w 3 2 J BL ZA D CONTROL OF THE TEMPERATURE OF SUPERHEATED VAPOR July 26, 1960 Filed April 13, 1953 CONTROL OF THE TEMPERATURE OF SUPERHEATED VAPOR John Blizard, Garden City, N.Y., assignor to Foster Wheeler Corporation, New York, N.Y., a corporation of New York Filed Apr. 13, 1953, Ser. No. 348,235

8 Claims. (Cl. 122-479) This invention relates to the generation of superheated vapor and more particularly to the control of the temperature of superheated vapor.

. The present invention provides a method of and apparatus for controlling the temperature of superheated vapor by varying the quantity of moisture in said vapor when it is being superheated and in which a portion of the saturated vapor from the vapor generator is condensed before its admission to the superheater. The portion of saturated vapor condensed consists of small droplets in suspension in the vapor which is introduced into the superheater inlet or at a point intermediate the inlet and outlet of the superheater.

The invention will be disclosed as applied to the control of superheated steam temperature, but it will be understood that the invention is capable of application to the temperature control of vapors generally.

In accordance with the present invention, a portion of saturated vapor leaving the steam and water drum of a vapor generator is condensed by passing it into a heat exchanger in indirect heat exchange relationship with water taken from the drum which water is cooled below the saturation temperature in the drum by reducing its.

pressure. The steam with its water content passes from the heat exchanger to the superheater wherein a portion of the heat input to the superheater is utilized to evaporate the water content. By varying the portion of steam condensed in the heat exchanger, the temperature of the steam leaving the superheater may be controlled as desired.

The invention will be. understood from the following description when considered in connection with the accompanying drawings in which:

Fig. 1 is a vertical sectional view illustrating the upper portion of a steam generator embodying one form of the invention, and

Fig. 2 is a view similar to Fig. 1, but more or less diagrammatic, illustrating another form of the invention. 1 Like characters of reference refer to the same or similar parts throughout the views. Referring to the drawings, the steam generator of the present invention comprises a setting having a combustion chamber 11 therein with a front wall 12 (Fig. 2) and a rear wall 13. The front wall 12 is inclined inwardly "atthe top thereof, as shown in Fig. 2, to form a roof 14 above which a steam and water drum 15 is positionedin substantially vertical alignment with rear wall 13; The walls of the combustion chamber 11, are lined with water wall tubes, the front wall 12 being lined with tubes 16, which connect at the upper end thereof with the bottom of drum 15, while the reai wall 13 is lined with water wall tubes 17 also connected at the upper end thereof with the bottom of steam drum 15. Side wall 18 is lined with riser tubes 19, connected at their upper end 'with a header 20. Header 20, in turn, communicates with drum 15 through tubes 21. A side wall, not shown, opposite wall 18 is also lined with water wall tubes which Patented July 26, 1960 connect with an upper header similar to header 20, not shown and which also communicates with drum 15. The riser tubes 16, 17 and 19 are connected at their opposite ends with headers, not shown, which headers receive feed water through downcomers 21'. Downcomers 21' are in communication with drum 15 through a plurality of other downcomers 23 and receive water from drum 15 through said other downcomers.

Rear wall 13 extends upwardly a distance short of the drum 15 and roof 14 thereby providing a gas outlet 24 for the chamber 11 across which outlet the upper portion of water wall tubes 17 extend. Gas outlet 24 communicates with a downwardly inclined gas passage or heating zone 25 which passage or zone connects with a vertically extending passage 26 (Fig. 2). At the end opposite that which communicates with passage 25, the passage 26 is in communication with a flue 27.

A superheater comprising an inlet section 28, an intermediate section 29 and an outlet section 30 is disposed in the path of gases flowing through passage 25 from chamber 11 through gas outlet 24. The inlet section 28 receives steam from an inlet header 31. Intermediate section 29 of the superheater is in communication with inlet section 28 through an intermediate header 32 and with outlet section 30 through header 33. Superheated steam is withdrawn from the superheater through an outlet header 34 which receives steam from outlet section 30. A secondary steam generating section, not shown, is in communication with drum 15 through riser tubes 35 connected to a horizontal header 36 (Fig. 2). Feed water for the vapor generator of the present invention is fed to drum 15 through a feed water pipe 37 disposed adjacent the bottom of the drum and extending longitudinally therein.

Saturated steam from drum 15 flows into a heat exchanger 39 through a saturated vapor line 38 While a mixture of steam and condensate passes to superheater inlet header 31 through a superheater inlet conduit 40.

As shown, heat exchanger 39 comprises a substantially vertically extending cylindrically-shaped shell 41 having a plurality of vertically extending tubes 42 disposed therein which tubes are mounted at the opposite ends thereof in horizontal tube sheets 43 in a fluid-tight manner. The tube sheets are secured to the inner periphery of the shell in a fluid tight manner and are in spaced relationship with the opposite ends of the shell thereby providing between them in the shell a liquid chamber 41' separated from the remainder of the interior of the shell in a fluid-tight manner. Dish-shaped heads 44 and 45 are secured respectively at the upper and lower ends of the shell in spaced relationship with tubesheets 43, to enclose said ends. The space at the upper end of the shell provides a steam inlet chamber 46 while the space at the lower end of the shell provides an outlet chamber 47. Outlet chamber 47 is in communicaiton with an induction nozzle 49 through steam outlet connection 48 in head 45.

Nozzle 49 has a steam mixture chamber 50 with an inlet 51 and an outlet 52. A converging nozzle portion 53 is disposed centrally in chamber 50 so as to form an annular reduced pressure passage 54 around the nozzle.

' Communicating with the liquid chamber 41' in shell 41 is a saturated water conduit 55, which conduit also communicates with steam and water drum 15 below the normal water level therein. A valve 56 controls the flow of water from drum 15 to chamber 41' in shell 41 as will herinafter be fully described. The water level in exchanger 39 is regulated by opening or closing valve 56 by any conventional regulating means, such as a float valve mechanism 57 which is illustrated diagrammatically in the drawings. In communication with the upper portion of chamber 41' above the normal water level therein,

is a reduced pressure line 58 which is also connected to inlet 51 of induction nozzle 49. Pressure valve 59 in line 58' is regulated by control means 60, which is responsive to the temperature of superheated vapor at the superheater outlet header so as to operate valve 59 as will hereinafter be fully set forth.

In normal operation of the embodiment of the invention illustrated in Fig. 1, saturated steam passes out of drum 15 through vapor line 38 into inlet chamber 46 of the heat exchanger thereafter flowing into tubes 42 wherein said steam passes in indirect heat exchange relationship with water from drum 15 in chamber 41 which enters said chamber through water valve 56 in conduit 55.

Float valve mechanism 57 is set so as to close valve 56 when the water in chamber 41' of heat exchanger 39 has reached a predetermined level thereby preventing further flow of water from drum 15 into chamber 41 through conduit 55 and so as to open valve 56 to permit flow of- Water into chamber 41' from drum 15 when the level of water in said chamber falls below a predetermined level. Water in chamber 41' is at a temperature below the drum saturation temperature because of a reduction in its pressure as it passes into the exchanger. As the steam flows downwardly in tubes 42, a portion thereof is condensed by passage of said steam in indirectheat exchange relationship with water in chamber 41'. The steam with its condensate content passes out of the lower end of the tubes through outlet chamber 47 into converging nozzle 53. The steam pressure is reduced in outlet chamber 47 and its velocity increased by connection 48'. Pressure valve 59 is opened and a flow of steam is induced from above the water level in chamber 41 by the low pressure steam ejected from the converging nozzle 53, the steam flowing out the heat exchanger to mixing chamber 50 in nozzle 49 through line 58 and inlet 51 of nozzle 49. In chamber 50, the steam with its water content flowing from drum 15, and the steam flowing from chamber 41' of the heat exchanger, are admixed, thereafter passing outwardly of outlet 52 of nozzle 45 through conduit 40 to superheater inlet 31 wherein the water content is evaporated and the steam is superheated.

If the temperature of the superheated steam leaving the superheater exceeds a predetermined value, control means 60, which is responsive to the temperature of superheated steam at the superheater outlet, actuates pressure valve 59 in line 58 toward its open position thereby permitting an increased flow of steam to pass from the upper part of chamber 41 through line 58 into steam mixture chamber 50 in nozzle 49 which flow is induced by the action of nozzle 53. Increased flow of steam from the upper part of chamber 41' through line 58 causes a reduction of the pressure and the temperature of the water in said chamber thusly increasing the rate of condensation of steam flowing through tubes 42 of the exchanger. The steam with the increased quantity of condensate therein passes from tubes 42 through outlet chamber 47 into outlet connection 48 thence through nozzle 53 into chamber .50 of induction nozzle 49 whence it flows into superheater inlet header 31 through conduit 40 thereby to reduce the temperature of the steam superheated in said superheater.

If the temperature of the superheated steam falls below the predetermined value, control means 60 actuates pressure valve 59 in line 58 toward its closed position thereby decreasing the flow of steam from the upper part of chamber 41' through line 58 into steam mixture chamber 50. Decreased flow of steam from the upper part of chamber 41' through line 58 causes an increase in thepressure and temperature of water in said chamber thusly decreasing the rate of condensation of steam flowing through tubes 42 of the exchanger. The steam with the decreased quantity of condensate therein passes from tubes 42through outlet chamber 47 into outlet connection 48 thence through nozzle 53 into chamber 50 of induction nozzle 49 whence it flows into superheater inlet header 31 through conduit 40 thereby causing the temperature of the steam superheated in said superheated steam to rise to said predetermined value due to the lesser amount of condensate in said steam entering the superheater.

U-pon an increase in the flow of steam through tubes 42, chamber 47 and connection 48 the pressure of steam leaving the converging nozzle 53 of the induction nozzle 49 will decrease thus lowering the pressure and temperature of the water in heat exchanger chamber 41' by in ducing a greater flow of steam. past valve 59, in line 58 thereby increasing the desuperheating effect of this arrangement. This is desirable since, in general, the superheated steam temperature of steam superheated in a steam generator not having a superheated steam temperature control increases with the rate of steam generated.

The temperature of the superheated steam may also be controlled by operating the water valve 56 to raise or lower the water level in the heat exchanger to vary the pressure and temperature of the water to produce a cooling efiect on the steam passing through the heat exchanger tubes from drum 15. Controller 57, instead of being a water level responsive controller, will be a temperature responsive controller which is responsive through a line 57" to the temperature of the superheated steam at superheater outlet 34 and is so constructed and arranged as to operate valve 56 toward its open position and increase the level of water in chamber 41 when the temperature of the superheated steam increases beyond a predetermined value therebyproducing a greater cooling effect on the steam passing through tubes 42 and increase the condensate content of steam flowing to the superheater thereby reducing the temperature of the steam superheated therein. Controller 57 is also constructed and arranged to operate valve 56 toward its closed position when the temperature of the steam superheated in the superheater falls below a predetermined value which reduces the water level in chamber 41 thereby reducing the cooling effect on the steam flowing through tubes 42' which results in a lesser condensate content in the steam flowing to the superheater from heat exchanger 39 so that the temperature of the steam superheated in said superheater will rise to said predetermined value.

Referring to Fig. 2, this embodiment of the invention is similar to the embodiment shown in Fig. 1 except that there is no induction nozzle 49 between superheated inlet conduit 40 and pressure line 58. Instead, reduced pressure line 58 is connected to superheater intermediate header 32 and a saturated vapor by-pass line 61 is provided which communicates with saturated vapor line 38 and superheater inlet header 31'.

In operation the embodiment of the invention illustrated in Fig. 2 is similar to that illustrated in Fig. l. The steam passes out of drum 15 through line 38 into heat exchanger 39 thence through the tubes 42 in the heat exchanger. Valve 56 in conduit 55 is controlled to permit water to flow from the drum 15' into the water space of the exchanger until said Water reaches a predetermined level therein the operation of valve 56 being controlled as in-the Fig. 1 embodiment of the invention. The water air chamber 41' is-cooled below the drum saturation temperature because'of a reduction in its pressure as it flows into the exchanger. A portionof the steam passing through the exchanger tubes 42 is condensed by passing in indirect heat exchange relationship with the cooled saturated water thereafter flowing to inlet header 31 of the superheater through steam conduit 40.

Pressure valve 59 in line 58 is opened to decrease or closed to increase the pressureand temperature in the heat exchanger chamber 41 by control means 60; which is responsive through line 61' to the temperature of steam superheated in the superheater, thereby passing steam above the water level in. chamber 41' of heat exchanger 39 through line 58 to intermediate header 32 which results in condensing a greater or lesser portion, respectively of the steam passing through the heat exchanger trom drum 15.

For example, when the temperature of the steam leaving the superheater exceeds a predetermined value, control means 60 actuates pressure valve 59 toward its open position to permit an increased flow of steam to pass from the upper part of chamber 41' to intermediate superheater header 32 which causes an increased desuperheating effect on the steam being superheated in superheating sections 29 and 30. Increased flow of steam from the upper part of chamber 41 causes a reduction of the pressure and temperature of water in said chamber thusly increasing the rate of condensation of steam flowing through tubes 42. The steam flowing from tubes 42, outlet chamber 47, line 40 to superheater inlet 31 will, therefore, have an increased amount of condensate therein which reduces the tempearture of the steam superheated in the superheater. Should the temperature of the superheated steam fall below said predetermined value, control means 60 actuates pressure valve 5 9 toward its closed position which decreases the flow of steam firom chamber 41' to intermediate header 32 thereby decreasing the desuperheating effect in sections 29 and 30 of the superheater. Decreased flow of steam from chamber 41' results in an increase in temperature and pressure in said chamber thusly decreasing the rate of condensation of steam flowing through tubes 42 so that steam passing to superheater inlet header 31 has less condensation therein which results in an increased temperature in the steam superheated in said superheater.

A by-pass steam line 61 having a control valve 62 is used for by-passing steam around heat exchanger 39 and for passing steam directly from drum 15 to superheater inlet header 31 when control of superheat temperature is not desired and only saturated steam is required.

With the arrangement of apparatus and the sequence of method steps provided by the above described inven tion, the desired superheat temperature is maintained substantially constant automatically by increasing or decreasing the moisture content of the steam being superheated the superheater to decrease the temperature of said steam to a predetermined value or increase said steam to the predetermind value, as the case may be. This is accomplished by an economical, eflicient and uncomplicated arrangement of apparatus and method steps.

Inasmuch as various changes may be made in the particular form, location and arrangement of the parts of apparatus disclosed and in the steps of the method and other sequences as disclosed without departing from the principles of the invention, it will be understood that the invention is not to be limited excepting by the scope of the appended claims.

What is claimed is:

1. A vapor generator comprising a vapor generating section, a superheater, a heat exchanger, means for introducing liquid from the generating section into the heat exchanger, means causing saturated vapors from the generating section to flow in indirect heat exchange relation-' ship with the liquid in the heat exchanger to condense part of the saturated vapor, the level of the liquid in the heat exchanger determining the quantity of vapor condensed, means for introducing the saturated vapor in admixture with substantially all of the resulting condensate produced in the heat exchanger into the superheater, and means responsive to the temperature of the vapor after superheating for controlling the level of the liquid in the heat exchanger to thereby control the quantity of vapor condensed and the temperature of the superheated vapor.

2. A vapor generator comprising a vapor generating section, a superheater, a heat exchanger having a cooling medium therein under pressure, the temperature of said cooling medium being a function of the pressure within 6 said heat exchanger, means for passing saturated vapors from the vapor generating section into the heat exchanger in indirect heat exchange relationship with the cooling medium therein to condense part of the saturated vapor, means for introducing the saturated vapor in admixture with the condensate produced in the heat exchanger into the superheater, means responsive to the temperature of the vapor after superheating to control the amount of vapor condensed and the temperature of the superheated vapor, and means communicating said vapor generating section with said superheater for bypassing the heat exchanger to provide for flow of said saturated vapor from said vapor generating section directly to the superheater when control of superheat temperature is not desired.

3. Apparatus of the class described comprising a superheater, a heat exchanger, a first chamber in said heat exchanger, means for passing unsuperheated vapors from a vapor generator into said first chamber, a second chamber in said heat exchanger in fluid-tight relationship with said first chamber and having -a cooling liquid therein under pressure and in indirect heat exchange with the unsuperheated vapors in the heat exchanger for condensing part of the vapor prior to superheating, a third chamber in said heat exchanger in fluid-tight relationship with said second chamber and communicating with said first chamber for receiving the condensate and the unsuperheated vapor, outlet means for discharging the condensate and the unsuperheated vapor from the heat exchanger for flow to the superheater, means operable by the flow of the unsuperheated vapor and condensate through said outlet means for effecting a generated vapor from said cooling liquid in said second chamber and the withdrawal of the generated vapor from the latter to vary the temperature of the cooling liquid, and means responsive to the temperature of the vapor after superheating for controlling the flow of generated vapor from the second chamber.

4. A vapor generator comprising a vapor generating section, a superheater, a heat exchanger, means for introducing liquid from the vapor generating section into the heat exchanger, means causing saturated vapors from the generating section to flow in indirect heat exchange with the liquid in the heat exchanger to condense part of the saturated vapor, means for mixing said saturated vapors and said condensate for how to the superheater, means operable by the flow of said mixture for efiecting a generated vapor from said cooling liquid in said heat exchanger and the withdrawal of .the generated vapor from the latter to vary the temperature of the cooling liquid, and means responsive to the temperature of the saturated vapor after superheating for controlling the flow of generated vapor from the heat exchanger.

5. A vapor generator comprising a vapor generating section, a superheater, a heat exchanger, means for introducing liquid from the vapor generating section into the heat exchanger, means causing saturated vapor from the generating section to flow in indirect heat exchange with the liquid in the heat exchanger to condense part of the saturated vapor, means for mixing said saturated vapor and condensate for flow to the superheater, means operable by the flow of said mixture for efiecting a generated vapor from the cooling liquid in the heat exchanger and the withdrawal of the generated vapor from the latter to varying the temperature of the cooling liquid, said means providing for the admixture of saturated vapor, condensate and generated vapor, means in communication with said last-mentioned means and with said superheater for conducting the last-mentioned mixture to the superheater, and means responsive to the temperature of the saturated vapor after superheating for controlling the flow of generated vapor from the heat exchanger.

6. A vapor generator comprising a vapor generating section, a heat exchanger, means for introducing liquid from the vapor generating section into the heat exchanger to provide a cooling liquid in the latter at a temperature below the saturation temperature of the liquid the vapor generating section, means causing saturated vapor from the vapor generating section to flow in indirect heat exchange with the liquid in the heat exchanger to condense part of the saturated vapor, means in said heat exchanger for collecting and mixing the saturated vapor and the condensate produced in said heat exchanger, a vapor mixture chamber in communication with the part of the heat exchanger containing the liquid, a nozzle communicating with said heat exchanger for conducting the mixture of saturated vapor and condensate from the heat exchanger into the vapor mixture chamber, said nozzle being disposed in said vapor mixture chamber to form a reduced pressure passage therein whereby the flow of said mixture through said nozzle inheater.

'7. A vapor genera-tor comprising a vapor generating section, a su'perh'eater, a heat exchanger comprlsing a shell having tube sheets therein defining a pair of spaced compartments and an intermediate compartment, said intermediate compartment being in fluid-tight relation- "ship with said pair of compartments, tubular members arranged within said intermediate compartment and communicating said pair of compartments with each other, means for introducing liquid from the vapor generating section into the intermediate compartment to provide a cooling liquid at a temperature below the saturation temperature of the liquid in the vapor generating section, means communicating said vapor generating section with one of said pair of compartments for providing passage of saturated vapor into the last-mentioned compartment, said tubular members passing the saturated vatime in indirect heat exchange with the liquid in said intermediate compartment to condense part of the saturated vapor, the other of said compartments receiving the condensate and the saturated vapor passing through 8 said tubular members, a vapor mixture chamber in communication with the intermediate compartment, a nozzle communicating with said other compartment for conducting the mixture of saturated vapor and condensate from the other compartments into the vapor mixture chamber, said nozzle being disposed in the vapor mixture chamber to form a reduced pressure passage therein, whereby the flow of said mixture through said nozzle induces a flow of generated vapor from said intermediate compartment to the vapor mixture chamber to thereby vary the temperature of the cooling liquid, control means responsive to the temperature of the superheated vapor for controlling the flow of generated vapor from the intermediate compartment, and means communicating said vapor mixture chamber with said superheater to provide for the passage of said mixture and said withdrawn generated vapor to the superheater.

8. The method of superheating vapor which comprises passing saturated vapor from a vapor generating zone to a condensing zone subjected to above atmospheric pres sures, condensing part of the saturated vapor in the condensing zone by indirect contact with a cooling liquid under pressure, introducing the saturated vapor in admixture with substantially all of the condensate pro duced in the condensing zone into a superheating zone to vaporize all of the condensate, varying the pressure of said cooling liquid to effect a generated vapor and to change the temperature of the cooling medium, and

withdrawing predetermined quantities of the generated vapor from the condensing zone in accordance with the temperature of the saturated vapor after superheating to control the final temperature of the superheated vapor.

References Cited in the file of this patent UNITED STATES PATENTS 2,207,646 Ploeg July 9, 1940 2,257,805 Kolling Oct. 7, 1941 2,319,223 Frisch May 18, 1943 2,604,085 Frisch July 22, 1952 FOREIGN PATENTS 394,417 Great Britain June 29, 1933 

